"I'm pleased to accept the appointment, and I will do my utmost to promote security and reforms in Ukraine, and strengthen the Ukraine-E.U. bond. I look very much forward to working with the Ukrainian authorities",Rasmussen posted on Facebook.

The ex-NATO Chief described the situation in Donbas as "alarming". But, he said, at the same time Ukraine need to continue to carry out reforms, including the fight against corruption. "In that respect, reinforced ties with the E.U. are essential", he stated.

Rasmussen is known for his support for Ukraine. In August 2014 Poroshenkoawarded him "for significant contribution to the development of cooperation between the state of Ukraine and the NATO, important support in defending the sovereignty, independence and integrity of Ukraine".

Moscow has already called this assignment "an enemy act against Russia".

"Ukraine is drifting towards NATO. The country is a stepping-stone (for NATO) against Russia, and it will be used if we or Ukraine itself don't oppose", Russian official Leonid Kalashnikov said in an interview with Interfax.

Kalashnikov added, "entering NATO would be a suicide for Ukraine".

Anders Fogh Rasmussen was NATO Secretary General from 2009 to 2014. He was replaced by Norwegian politician Jens Stoltenberg.